Allison S A, Potter M, McCammon J A
Department of Chemistry, Georgia State University, Atlanta 30303, USA.
Biophys J. 1997 Jul;73(1):133-40. doi: 10.1016/S0006-3495(97)78054-8.
In this work, boundary element methods are used to model the electrophoretic mobility of lysozyme over the pH range 2-6. The model treats the protein as a rigid body of arbitrary shape and charge distribution derived from the crystal structure. Extending earlier studies, the present work treats the equilibrium electrostatic potential at the level of the full Poisson-Boltzmann (PB) equation and accounts for ion relaxation. This is achieved by solving simultaneously the Poisson, ion transport, and Navier-Stokes equations by an iterative boundary element procedure. Treating the equilibrium electrostatics at the level of the full rather than the linear PB equation, but leaving relaxation out, does improve agreement between experimental and simulated mobilities, including ion relaxation improves it even more. The effects of nonlinear electrostatics and ion relaxation are greatest at low pH, where the net charge on lysozyme is greatest. In the absence of relaxation, a linear dependence of mobility and average polyion surface potential, (lambda zero)s, is observed, and the mobility is well described by the equation [formula: see text] where epsilon 0 is the dielectric constant of the solvent, and eta is the solvent viscosity. This breaks down, however, when ion relaxation is included and the mobility is less than predicted by the above equation. Whether or not ion relaxation is included, the mobility is found to be fairly insensitive to the charge distribution within the lysozyme model or the internal dielectric constant.
在这项工作中，边界元方法被用于模拟溶菌酶在pH值范围为2至6时的电泳迁移率。该模型将蛋白质视为具有任意形状且电荷分布源自晶体结构的刚体。在早期研究的基础上进行拓展，本工作在完整的泊松-玻尔兹曼（PB）方程层面处理平衡静电势，并考虑离子弛豫。这是通过迭代边界元程序同时求解泊松方程、离子输运方程和纳维-斯托克斯方程来实现的。在完整的而非线性PB方程层面处理平衡静电学，但不考虑弛豫，确实能改善实验迁移率与模拟迁移率之间的一致性，而包括离子弛豫则能进一步改善。非线性静电学和离子弛豫的影响在低pH值时最为显著，此时溶菌酶上的净电荷最大。在不存在弛豫的情况下，观察到迁移率与平均聚离子表面电势（λ₀）呈线性关系，并且迁移率可以用方程[公式：见原文]很好地描述，其中ε₀是溶剂的介电常数，η是溶剂粘度。然而，当考虑离子弛豫时，这种关系就不成立了，此时迁移率小于上述方程的预测值。无论是否考虑离子弛豫，发现迁移率对溶菌酶模型内的电荷分布或内部介电常数相当不敏感。
